The present invention relates to surgical instruments and in particular to surgical instruments that include openings for engaging projections to hold the surgical instrument in a particular position.
Many surgical instruments require fixing in a known position relative to a patient. One example is a cutting block. Cutting blocks are typically affixed to a patient's bone in a position such that they can guide cutting and resection of the bone surface for receiving an implant.
Existing cutting blocks are mounted to a patient's bone by engaging projections or pins in recesses. In some systems the projections extend from the cutting block and engage holes drilled in the bone. In other systems a fixed reference philosophy is used and the cutting block contains openings or holes that engage projections installed in the bone and which extend from the bone surface.
In a fixed reference philosophy, instrumentation is first used to determine the correct position for the projections on the bone. The projections are then inserted into the bone and used to mount the cutting block and hold it in the correct position relative to the bone by engaging the openings on the cutting block.
If the cutting block is only intended to be provided in one position relative to the projections then one set of openings is provided, with each opening in the set positioned to receive each projection. Alternatively, the cutting block may be mounted in a number of different positions relative to the projections. For example, the surgeon may need to alter the position of the cut slightly from the measured position without having to reposition the projections. In that case the cutting block may include a number of sets of openings for engaging the projections.
Placing the cutting block on the projections is difficult. The projections extend from the bone surface in a direction towards the cutting block. As the surgeon looks at the cutting block and moves it towards the mounting projections, the position of the projections relative to the openings is obscured by the cutting block itself.
To overcome this problem, surgeons may attempt to view the bone surface while placing the cutting block on the pins. However, it can be difficult to position the patient such that this view is available, or it can require unacceptable manipulation of the patient. Even if the surgeon can view the projections, surgical lighting is designed for viewing from the direction the cutting block is installed. It can be difficult to identify the projections and openings accurately against the backdrop of the bright surgical lighting.
To assist in placement of the projections in the openings it is known to provide chamfers on the edges of the holes. These widen the entrance to the hole slightly, assisting alignment of the pins. However, due to design constraints the chamfer can be very small. For example, the space available between adjacent holes may constrain any chamfer so that it is over a radial distance of less than a millimeter. This limits the usefulness of the chamfer.
If the cutting block is placed on more than one projection, for example a pair of projections, it can be difficult to place the cutting block if the projections have not been installed in precisely the correct position. For example, one of the projections may be at a slight angle relative to another of the projections so that they do not align exactly with the openings.
Accordingly, the present invention provides a recess or slot which extends linearly from an opening for engaging a projection such as a pin. The recess may extend from the opening to the edge of the instrument.
The recess can be used as a track to guide a projection to an opening, increasing the area of the instrument that can be used to locate the projection in the correct position. The recess acts as a guide for the projection to enter the opening by providing tactile feedback to guide the projection towards the opening. If the recess also extends to the edge of the instrument, the recess may be visible more easily when the surgeon is installing the instrument providing visual as well as tactile feedback.